Scientists have known that shy toddlers often have delayed speech, but a new study by the University of Colorado Boulder shows that the lag in using words does not mean that the children don’t understand what’s being said.

The nature of the connection between behavioral inhibitions—such as shyness or fearfulness—and delayed language acquisition has not been well understood.

The new study, published in the journal Child Development, tests four possible explanations for the association: that shy children practice speaking less and so their speech becomes delayed, that children with delayed speech become shy because they have difficulty talking, that shy children understand what’s being said but are simply reticent to speak, and that shy children’s speech is actually normal while outgoing children’s speech is above average.

The research team, from CU-Boulder’s Institute for Behavioral Genetics (IBG) and the Department of Psychology and Neuroscience, found consistent evidence to support only the hypothesis that shy toddlers were delayed in speaking but not in understanding.

“Behaviorally inhibited children who may not be speaking much shouldn’t be underestimated,” said Soo Rhee, an author of the study and an associate professor of psychology and neuroscience. “Parents and teachers should be aware that they may need to be encouraged more in their expressive language development.”

For the study, the researchers looked at information collected on 408 sets of twins at 14, 20 and 24 months of age, when children’s language skills are rapidly expanding. The data on inhibition and speech characteristics of the 816 toddlers came from parent reports and researcher observations. Notes were made both of the child’s ability to repeat sounds and answer questions as well of the child’s ability to follow directions.

The research team looked for patterns in how the children’s behavior changed over time, noting whether an increase in shyness, for example, followed or preceded a delay in speech. The result—that shy toddlers understand more than they indicate through talking—is both good news and bad news.

“It’s good news that the children are not delayed in language acquisition,” Rhee said. “But not being willing to speak may still have consequences.”

Past studies have shown that delayed speech can lead to a number of negative outcomes later in life, including poor self-regulation and social difficulties.

The idea for the research project came from CU-Boulder undergraduate student Deepika Patel, who proposed the idea for her honors thesis and who is a co-author of the study. The first author of the study is Ashley Smith Watts, a doctoral student in psychology and neuroscience. Other CU-Boulder co-authors are Robin Corley, a senior research associate at IBG; Naomi Friedman, faculty fellow at IBG and an assistant professor of psychology and neuroscience; and John Hewitt, director of IBG and professor of psychology and neuroscience. JoAnn Robinson of the University of Connecticut is also a co-author.

The study was funded by the MacArthur Foundation and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Quotes

“Behaviorally inhibited children who may not be speaking much shouldn’t be underestimated,” said Soo Rhee, an author of the study and an associate professor of psychology and neuroscience. “Parents and teachers should be aware that they may need to be encouraged more in their expressive language development.”